This invention relates to a multiband aerial, especially suitable for application to a motor vehicle window such as a front windshield or windscreen window.
The aerial assembly, or rather the aerial circuit, in accordance with the invention, and the window on which said circuit is applied, is usually just called the "aerial window".
Multiband aerials for reception of signals both in the ultrashort wave band (FM), and in the short, medium and long wave band (AM) are already well known in many and various configurations, and are increasingly finding general application, replacing the fishpole type aerials hitherto used on motor vehicles.
The circuits of said multiband aerials are generally applied on the window by means of a silk screen printing process on a glass frit containing a metallic conductor, followed by annealing, or else by the imbedding of a conductor wire in the plastic film interposed between two glass panes which form the window, and which window or window pane is operatively mounted in a corresponding motor vehicle window opening in conventional manner, e.g. as a windshield or windscreen window or window pane (see FIG. 5).
The hitherto known multiband aerial configurations normally consist of central elements on the windshield or windscreen window for FM reception, and side elements, going along the edge of the windshield or windscreen window, for AM reception; these elements are then interconnected to the cable leading from the aerial to the radio receiver.
Particularly widely diffused, among the various aerial configurations adopted, are those described in Italian Pat. No. 945.948 (to Saint Gobain) consisting of a vertical conductor of fishpole or T form for reception in the ultra short wave band (FM) arranged along the windshield or windscreen window centre line, and of a separate conductor for reception in the short, medium and long wave band branching from the signal pick up point into two arms which follow along the windshield or windscreen window edge.
Also worthy of note, thanks to its special characteristics, is the aerial configuration according to Italian patent application no. 20387 A/79 (to Fabbrica Pisana S.p.A.) consisting of vertical segments interconnected to horizontal segments, wherein the latter are chiefly confined to the top part of the windshield or windscreen window, and their horizontalness depends on the slope of the windshield or windscreen window top edge.
Lastly mention should be made of the aerial configuration, outstanding for its novelty, according to French patent application No. 7338052 (publication no. 2.205.755) (to Flachglas A.G. Delog-Detag). This aerial consists of double vertical and horizontal elements interconnected at the signal pickup point.
All hitherto known aerial configurations, including the above described ones, have the various conductors forming the aerial, that is for FM and for AM, converging on one or more points which are connected one to the other, and therefore "in parallel".
Hence in these known configurations, the signal received from the central aerial segment is then summed in phase with that received from the peripheral aerial segment, in order to improve aerial performance in AM or FM.
These already known aerial configurations however possess two rather appreciable drawbacks: firstly, it is not possible in actual practice to vary the signal pickup position on the window, while at the same time keeping the configuration geometry unvaried, as the conductor element lengths are interdependent on ratios which are in relation to the wave lengths received; secondly, all the aerial configurations hitherto described are highly directional.
This means that the aerial receives radio signals at an acceptable degree only when it is oriented towards the transmitter within certain angles, and its reception properties are considerably diminished when the angle of orientation is over 180.degree. and below 360.degree..